This type of cutoff, which is described, for example, in U.S. Pat. No. 3,858,040, is specifically adapted to a dipped beam of the type required, for example, in the United States of America and defined by the standard SAEJ 579 C.
In order to satisfy this standard, the cutoff profile is approximately defined on a standardized screen by two horizontal half-lines situated on either side of the headlight axis, with the right-hand half-line being at horizon level and with the left-hand half-line being offset below the horizon by about 1.5%. In addition, the specified region of maximum illumination is offset to the right from the axis of the headlight.
Beams meeting such standards are generally obtained by means of a headlight comprising a lamp having a transverse filament and co-operating with a parabolic mirror or reflector having a relatively long focal length, so as to reduce the height of the beam and thus minimize the amount of thickening required in the closure glass to create light-deflecting prisms.
Proposals have also been made for headlights having a lamp with an axial filament which is focused in a parabolic reflector wich is tilted downwardly to reduce the amount of deflection required of the prisms in the closure glass, thereby reducing the required thickness of glass. Above-mentioned U.S. Pat. No. 3,858,040 describes examples of both types of headlight.
However, in both of the embodiments described in said patent, it is necessary to use a parabolic reflector having a long focal length of about 29 mm to 32 mm, which therefore collects relatively little flux.
In order to remedy this low light yield, Cibie has proposed in its U.S. patent application No. 067,432 of June 25, 1987, a continuation of U.S. Application 755,070 of July 15, 1985 entitled "Dipped headlight for Motor Vehicle", a headlight having a reflector which is complex in shape and suitable for forming images of the filament below a cutoff line which extends generally horizontally, which enables short focal lengths to be used, and which consequently collects a much greater amount of flux. More precisely, such a headlight comprises an axial filament lamp emitting light freely in all directions about the filament, a reflector having an axis extending beneath the axis of the filament and parallel thereto, said reflector having a surface without discontinuity, and a closure glass placed in front of the reflector and suitable for spreading said beam in a horizontal direction. However, regardless of the practical embodiment of said headlight, the mirror must be turned to the right in order to obtain the required rightwards offset of the bright spot.
Unfortunately, it is generally undesirable to turn a mirror in this way, and in particular such turning constitutes a major obstacle in the implementation of headlights comprising two mirrors which are injected as a single part. One such headlight is shown diagrammatically in horizontal section in FIG. 1. It comprises a one-piece reflector 10 comprising a first mirror 10a for the dipped beam with an axis 12a which is offset to the right (downwards in the figure) by an angle .delta., and a second mirror 10b for the high beam which is integral with the first and whose axis 12b extends straight ahead.
The unmolding of such a two-part mirror is hindered by the fact that the dipped beam and main beam lamps 14a and 14b are received by supporting collars 13a and 13b which necessarily extend along the above-mentioned axes 12a and 12b, which means that they cannot be unmolded along the same unmolding axis. It is therefore necessary to use a mold of special design for making such a two-mirror headlight, and in particular the mold requires slides which are expensive and difficult to implement.
Another drawback in implementing the above-mentioned patent application lies in the fact that the tilting to be given to the dipped beam reflector is a function of the focal length used and of the optical characteristics of the closure glass. More precisely, the reflector must be turned sideways through an angle corresponding to one half of the angular width of the images that contribute to the bright spot. Unfortunately, the width of these images depends on the size of the zones in the closure glass which are used for light-concentration purposes, as well as on the focal length of the reflector, and these parameters are a function of the space available in the vehicle for housing the dipped headlight, and more generally on the design requirements of the vehicle.
The present invention seeks in particular to avoid the unmolding problem by providing a dipped headlight which does not require its axis to be turned to the right in order to obtain an offset concentration spot. The filament, and thus the lamp, therefore remains parallel to the road axis and a two-mirror headlight including such a dipped headlight can easily be made at moderate expense with both mirrors being unmolded along the same axis.